I'm at exactly the opposite end: a student transitioning from RAA to GA/PPL with a view to continuing through to CPL. I've gone from a Gazelle (RAA) to a Cherokee (GA, only a quick stint) to a C-172RG (GA).
Learning in the Cherokee would have been pointless, I think. The transition from the Gazelle to the Cherokee was fairly straightforward, and I saved plenty of money by starting on the Gazelle.
I'm not sure about learning in the C-172RG. It's certainly not a trivial transition from either of the other two. Would I have become confident in it faster if I'd started in it? Maybe, maybe not. It definitely would have cost a lot more (about twice as much per hour compared to the Gazelle).
Quite apart from that, starting with RAA gives you a good "low-cost" (to the extent that anything in aviation is low-cost) introduction. If you get to five hours in and you don't like it, you've only spent a thousand dollars or so. After twenty hours, if you're happy with your capabilities and don't really feel like going further, you can do the test to get your RAA certificate and stop there. Total cost: not much more than $4K. If you're still loving it and itching to fly more challenging planes, you can continue straight on towards a PPL.
On the other hand, if you'd gone straight to GA then all those initial hours cost a lot more - and in a complex aircraft it'll probably be a fair bit longer before you really start to enjoy it. More money, less reward.
For me, that made RAA a much better option. If I'd spent $2000 in the C-172RG and still felt that I was nowhere near being ready to fly it, I'd probably have given up. Instead I spent $2000 for twice as much time in the Gazelle, and at the end of that I'd been going solo for a few hours and was having a great time. Now that I'm in the C-172RG, I'm sure that this is a good idea, and therefore I'm not too concerned about putting lots of money towards it.